Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have been used in a wide variety of solvent applications such as drying, cleaning (e.g., the removal of flux residues from printed circuit boards), and vapor degreasing. Such materials have also been used in refrigeration, as blowing agents and in heat transfer processes.
For example, polyurethane and polyisocyanurate foams have been produced using trichlorofluoromethane (CFC-11), as the blowing agent of choice. Phenolic foams have heretofore generally been expanded with blends of trichlorofluoromethane (CFC-11) and 1,1,2-trichlorotrifluoroethane (CFC-113) blowing agents. Thermoplastic foams are usually expanded with dichlorodifluoromethane (CFC-12).
Further, many smaller scale hermetically sealed, refrigeration systems, such as those used in refrigerators or window and auto air conditioners, use dichlorodifluoromethane (CFC-12) as the refrigerant. Larger scale centrifugal refrigeration equipment, such as those used for industrial scale cooling, e.g., commercial office buildings, generally employ trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) or 1,1,2-trichlorotrifluoroethane (CFC-113) as the refrigerants of choice.
Aerosol products have employed both individual halocarbons and halocarbon blends as propellant systems. Halocarbons have also been used both as solvents and propellant vapor pressure attenuators, in aerosol systems.
While these materials were initially believed to be environmentally-benign, they have now been linked to ozone depletion. According to the Montreal Protocol and its attendant amendments, production and use of CFCs must be discontinued (see, e.g., P. S. Zurer, "Looming Ban on Production of CFCs, Halons Spurs Switch to Substitutes," Chemical & Engineering News, page 12, Nov. 15, 1993).
The characteristics sought in replacements, in addition to low ozone depletion potential, typically have included boiling point ranges suitable for a variety of solvent cleaning applications, low flammability, and low toxicity. Solvent replacements also should have the ability to dissolve both hydrocarbon-based and fluorocarbon-based soils. Preferably, substitutes will also be low in toxicity, have no flash points (as measured by ASTM D3278-89), have acceptable stability for use in cleaning applications, and have short atmospheric lifetimes and low global warming potentials.
Certain perfluorinated (PFCs) and highly fluorinated hydrofluorocarbon (HFCs) materials have also been evaluated as CFC and HCFC replacements in solvent applications. While these compounds are generally sufficiently chemically stable, nontoxic and nonflammable to be used in solvent applications, PFCs tend to persist in the atmosphere, and PFCs and HFCs are generally less effective than CFCs and HCFCs for dissolving or dispersing hydrocarbon materials. Also, mixtures of PFCs or HFCs with hydrocarbons tend to be better solvents and dispersants for hydrocarbons than PFCs or HFCs alone.
Hydrofluorocarbon ethers (HFE) have also been evaluated as CFC replacements in certain applications. For example RITE in the Conference Proceedings of the International CFC and Halon Alternatives Conference, Oct. 24-26, 1994 discloses several hydrofluorocarbon ethers as possible CFC replacements and discusses various properties of these compounds. Methoxy-perfluoropropane was mentioned amongst the many hydrofluorocarbon ethers in this disclosure. WO96/22356 discloses HFEs for use in cleaning of substrate surfaces. WO96/22356 mentions methoxy-perfluoropropane and optional mixtures thereof with various solvents. WO96/22129 mentions the use of HFEs and in particular methoxy-perfluoropropane in fire extinguishing compositions. Published Japanese Patent Application (Kokkai) 8-259930 discloses the use of perfluoropropyl methyl ether as a transport fluid.
While HFEs are excellent candidates as CFC and HCFC replacements, they may not always have all the desired properties for particular applications. For example, in replacing a CFC as a refrigerant, an HFE may not have sufficient solvency for lubricants that are generally admixed with the CFC. Accordingly, mixtures of HFEs with other organic components are being considered. Such mixtures are preferably azeotropic compositions.
Many azeotropes possess properties that make them useful as CFC and HCFC replacements. For example, azeotropes have a constant boiling point, which avoids boiling temperature drift during processing and use. In addition, when a volume of an azeotrope is used as a solvent, the properties of the solvent remain constant because the composition of the solvent in the vapor phase does not change. Azeotropes that are used as solvents also can be recovered conveniently by distillation.
For example, WO93/11201 discloses azeotropic compositions of hydrofluorocarbons and hydrofluorethers as refrigerants. U.S. Pat. No. 5,023,009 discloses binary azeotropic compositions of 1,1,1,2,3,3-hexafluoro-3-methoxypropane and 2,2,3,3,3-pentafluoropropanol-1.
Azeotropic compositions that involve one or more CFCs also have been considered to tailor properties of CFCs for particular demands in some applications. For example: U.S. Pat. No. 3,903,009 discloses the ternary azeotrope of 1,1,2-trichlorotrifluorethane with ethanol and nitromethane; U.S. Pat. No. 2,999,815 discloses the binary azeotrope of 1,1,2-trichlorofluoroethane and acetone; U.S. Pat. No. 2,999,817 discloses the binary azeotrope of 1,1,2-trichlorotrifluoroethane and methylene chloride.
Despite the fact that many azeotropes are known in the art, there continues to be a further need for azeotropic compositions which have desirable end-use characteristics. Unfortunately, as recognized in the art, it is in most cases not possible reliably to predict the formation of azeotropes, a fact complicating the search for new azeotropic compositions.